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Thread: Black tank flush leak

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    Junior Member
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    Black tank flush leak

    I have 24 ft Northtrail with black tank flush option.When I use it it leaks bad underneath instead of pouring out the dump valve.I have an enclosed underbelly and can't access to see what's going on.Any suggestions on troubleshooting this issue would be appreciated.

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    Senior Member Bogie's Avatar
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    Re: Black tank flush leak

    There is a good chance the back flow vacuum break has failed. That seems all to common in RV's. I can't say where yours is located, but often they are behind the shower. If that's where it is, you usually gain access to it by removing the shower valve set.

    Perhaps someone with your model will chime in and tell you where it is.

    The routing of the back flush usually goes from the hose connection then up a few feet to the vacuum break, then down to the black tank. If it's not the vacuum break, then you may have to pull down part of the underbelly, or maybe cut a small inspection hole to look for the leak.

    Here is a picture of what it looks like.

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    Re: Black tank flush leak

    That was exactly the problem.Mine was located under the sink.Ordered a new one on Amazon.Thanks much for the info.

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    Re: Black tank flush leak

    Had mine fail on two out the the three units I have owned over the last few years. I decided to replace this cheap plastic valve with a brass pex ball valve. Obviously I have to manually turn the valve on and off when I flush the tank, but it will never fail and flood the RV again.
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  5. Print this Post   #5

    Re: Black tank flush leak

    Not sure if my problem is similar but when I hook up my hose to the black tank flush it flushes ok but when I remove the hose I get water gushing back out the inlet untill the back pressure is gone from the flush. It soaks everything in my wet bay. Lol guess that why they call it a wet bay. Is this normal or is this a failed back flow preventer.? Thanks


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    Moderator danemayer's Avatar
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    Re: Black tank flush leak

    Quote Originally Posted by shawnmuir View Post
    Not sure if my problem is similar but when I hook up my hose to the black tank flush it flushes ok but when I remove the hose I get water gushing back out the inlet untill the back pressure is gone from the flush. It soaks everything in my wet bay. Lol guess that why they call it a wet bay. Is this normal or is this a failed back flow preventer.? Thanks


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    Are you certain the water is actually getting into the black tank when you use the flush inlet? I ask because water gushing back out when you disconnect sounds like maybe the connections to the anti-siphon valve are reversed.

    Or perhaps one of the water lines is kinked.


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  7. Print this Post   #7

    Re: Black tank flush leak

    I use a clear sewer connector so I can watch to see if it coming clear and the water does rush out when rinsing so I assume the tank is being flushed.


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  8. Print this Post   #8
    Prolifically Gabby Member JohnDar's Avatar
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    Re: Black tank flush leak

    Quote Originally Posted by shawnmuir View Post
    Not sure if my problem is similar but when I hook up my hose to the black tank flush it flushes ok but when I remove the hose I get water gushing back out the inlet untill the back pressure is gone from the flush. It soaks everything in my wet bay. Lol guess that why they call it a wet bay. Is this normal or is this a failed back flow preventer.? Thanks


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    More likely the crappy plastic check valve in the tank flush inlet is broken and now nothing more than a hollow tube. Many years ago, the female connection on mine broke, so I replaced the entire fitting with a city water fitting with a brass check valve on it. What was supposed to be a check valve was a hollow tube. It was made by the same company that makes the cheap, poorly designed plastic Anti-Siphon valve. Oh yeah, the ASV on my rig also failed a couple of years ago, flooding the kitchen area. Ripped it out of the wall and put a brass SharkBite check valve in its place. RVIA be dammed, those valves are a disaster waiting to happen.
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    Senior Member mlpeloquin's Avatar
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    Re: Black tank flush leak

    Ger a Watts brass vacuum break valve. Get Shark Bite adapters for it.

    https://www.amazon.com/Watts-Technol...-4&tag=mh0b-20
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  10. Print this Post   #10

    Re: Black tank flush leak

    If an ASV is a Anderson Selector Valve I all ready replaced mine as I was getting water filling my storage tank without asking for it and replaced it with the new brass one. Why do they cheap out on important sections. Just keeps us RVers busy. Thanks for the reply I will look at that.


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    • TWR 17200 lbs
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    2014 Heartland Big Country 3070RE, 35'-0"
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